In recent years there has been explosive growth in the number of wireless devices in use. In fact, the rate of growth of wireless devices is increasing at a very fast rate. The increased use of wireless devices includes all types of portable computers, mobile computers, hand-held computers, so called personal digital assistants (PDAs) and numerous types of electronic organizers. Accompanying this increase in the use of wireless devices in an increasing demand for mobile data/voice services for use with these devices that is both flexible and simple.
A portion of these wireless devices can be considered ‘host systems’ from the viewpoint of the functionality and services they provide to a user. The host system can be connected to a regular conventional cellular handset via a cable or an integrated cellular communication system (CCS) and can be used for both voice and data. Many of the wireless devices available today are able to deploy some kind of data application. As a result of this, some cellular data services, in some cases, do not include voice capabilities.
In the case of an analog cellular communication system (ACCS), data is transferred by transmitting the analog signal generated by a voice band modern (e.g., V.32 bis). In the case of a digital CCS data is transferred by multiplexing the data bits to be transmitted into the bit stream and transmitting them through the digital modem.
Conventional cellular communications systems are typically implemented using dedicated hardware such as shown in FIG. 1. The cellular subscriber unit, generally referenced 10, is typical of prior art devices. The hardware making up the subscriber unit 10 performs several tasks including analog or digital cellular modem functions, analog voice band modem functions and performing voice codec functions. These functions are performed in part by a dedicated digital signal processor (DESP) that is part of the baseband module. The software for the DSP is stored in memory 20 which comprises read only memory (ROM).
There are several disadvantages to the implementation of the subscriber unit 10 described above. One disadvantage is that a cellular subscriber unit implementation that is based on dedicated hardware increases the cost of the finished product. Using dedicated hardware also increases the power consumption of the device which is increasingly a critical issue in the mobile devices market. There is tremendous pressure to design wireless products that are more powerful, provide increased functionality in a smaller size, utilize less power and have greatly increased battery life.
Another factor that is critical with cellular subscriber units is their physical size, wherein extra hardware crammed into the device, causing its dimensions to increase, is not desirable.
Yet another feature that is critical with cellular subscriber devices is the flexibility within a single device to work with different cellular standards Additional hardware is often necessary in order to achieve this goal. Adding data handling capabilities to an analog CCS via voice band modems requires additional hardware. This increases the cost of the unit in addition to increasing its size and power consumption.
A feature that is desirable in subscriber units is the ability to upgrade in a flexible manner. It is also desirable to be able to support multiple products within a product line using the same hardware. For example, the subscriber can be constructed to support a specific cellular standard, voice only, data only or voice plus data The ability to provide a flexible upgrade capability may be difficult if the hardware and firmware is fixed as is the case in conventional cellular subscriber units.
Another drawback to using the hardware implementation for the cellular subscriber unit is the difficulty in implementing complex modem techniques that serve to improve performance in connection with high speed data services, for example. Implementing complex modem techniques in hardware will impose additional cost, size and power consumption limitations.